Conventionally, known photoelectric conversion apparatuses include an apparatus which transfers a charge of a photoelectric conversion element to a floating diffusion region through a transfer MOS transistor and converts it into a voltage to read out.
Concerning such photoelectric conversion apparatus, Japanese Patent Application Laid-Open No. 2004-063498 discloses a configuration in which a signal charge is read out at a low voltage and no signal charges are left behind. Specifically, it is a photoelectric conversion apparatus that includes a first gate electrode approximately adjacent to one end of a photodiode region, a second gate electrode adjacent to the first gate electrode and a drain region approximately adjacent to one end of the second gate electrode.
However, according to the configuration disclosed in Japanese Patent Application Laid-Open No. 2004-063498, since a photodiode is formed deeply under the first gate electrode, and the photodiode and the drain region are situated close to each other when the size of pixel is reduced, a punch-through may be possibly produced in a bulk, resulting in an electrically conducting state.
Therefore, an object of the present invention is to provide a photoelectric conversion apparatus in which electrical connection between a photoelectric conversion element and a drain region can be controlled easily, and transfer efficiency of a charge from the photoelectric conversion element can be improved.